The invention relates to a method for producing a tube with a bent progression or with a bend embodied as a traverse progression as well as a preprocessed tube that can be used to produce a tube. The present invention particularly relates to a method and a preprocessed tube to produce such a tube made from metal.
Bent or curved metallic tubes are generally produced at first straight-lined and then the bends or curves are then implemented by processing the initially straight tube. This can occur at the facilities of the tube manufacturer or on site with the user. When relatively large bending radii are to be produced and the ratio of the diameter of the tube in reference to its wall thickness is not excessive the curves are usually created by bending the tube. The bending is limited, though, when very small bending radii are to be implemented to an intended folding of the tube, or when a thin-walled tube is bent having a large diameter. When several bends are to be created in a small space (aligned) in different spatial directions the bending of the tube is not practical, either.
Therefore, it is known alternatively to produce a bent section of the tube such that two miter cuts are inserted into the straight tube, creating two tube sections having miter cut surfaces extending along the faces of the cutting levels and a cutting wedge located therebetween, and after the removal of the cutting wedge the two tube sections are made to contact at their miter cut surfaces and welded together all around. A bend with a larger bending radius and/or bending angle can be produced in this manner by several slight folds in the form of a traverse progression.
Cutting out the cutting wedge by making two miter cuts, and the subsequent angular connection of the two thus produced tube sections with a following welding connection is more expensive than bending a tube, though. By cutting out the cutting wedge two separate tubes develop, which have to be carefully placed together and must be carefully aligned, particularly with regard to an axial distortion. In general, prior to welding the two tube sections together with a circular, water and air tight welding seam the tube sections carefully placed together and aligned must be preliminarily connected to each other via temporary welding spots, so that the alignment during the welding process is maintained. The alignment and particularly the placement of the welding spots can usually only be performed manually. When a bend is to be created having several transversely progressing folds placed adjacently, several individual tube sections develop, which renders the handling rather complicated and which may lead to mix-ups. The latter is of particular importance when no even bend in a single spatial direction is to be produced, but the folds of the transverse progression are aligned to different spatial directions, perhaps even with different bending radii.